A direct-IQ radio architecture comprises base band data modification, digital-to-analog conversion (DAC), and analog IQ-quadrature modulation to finally bring a complex I+jQ signal to radio frequency (RF). The IQ-modulator exhibits a DC-component, an amplitude error and also a phase error. Both of the branches (I and Q) of the IQ-modulator suffer from this imbalance.
In order to get a better power budget in the direct-IQ radio architecture for digital pre-distortion (to compensate for imperfections of the power amplifier), the analog IQ-modulator is foreseen to be driven by a higher input power. As a result, the mixer parts of the IQ-modulator tend to become inherently non-linear on top of the linear amplitude and phase imbalance.
Today, no specific solution exists as how to linearize an IQ-modulator. Absence of a linearizer gives rise to added unwanted signal inter-modulation due to high power usage of the IQ-modulator. There is a need to counteract the non-linearities in order to meet specifications and at the same time keep a good power efficiency budget.